Cathy Gordon and Alex Britton

The "horrific" story of how a teenage girl and her boyfriend plotted to brutally murder her mother and 13-year-old sister can be revealed for the first time after leading judges allowed the pair to be named.

Fifteen-year-olds Kim Edwards and Lucas Markham - believed to be Britain's youngest double murderers - have previously been protected by an order banning their identification.

But three Court of Appeal judges in London have now lifted the prohibition, meaning it can now be reported that the couple's victims were Edwards' mother, dinner lady Elizabeth Edwards, 49, and sister Katie.

The mother and daughter were stabbed in "brutal executions" as they slept at their home in Spalding, Lincolnshire, last April.

Over the course of the next 36 hours the "besotted" teenagers, then both 14, had sex, shared a bath and watched Twilight vampire films as they "revelled" after the killings.

Both were detained for life with minimum terms of 20 years last November by a judge at Nottingham Crown Court who said the case had ''few parallels in modern criminal history".

The restriction so far preventing their names being made public was overturned by Sir Brian Leveson, Mr Justice Blake and Mr Justice Lewis on Friday at the same time as they ruled that the minimum terms should be reduced to 17-and-a-half years.

Sir Brian announced that, as a result of the court's decision, "the names of these two young people are now capable of being reported", allowing the "full facts and circumstances" surrounding the case to be made public.

Describing it as an "exceptional case", Sir Brian said Markham and Edwards "clearly became besotted with each other". Both were unhappy in their respective homes.

Edwards held grudges against her mother and sister and Markham came to "share her grudges and hatred" towards them. They "jointly decided" to kill Edwards' mother and her "entirely innocent" sister.

Sir Brian said the facts of the case "cannot be properly understood without identifying that the appellants murdered the mother and 13-year-old sister of Kim Edwards".

No new material had been put before the court to "justify the conclusion that lifting anonymity would cause harm to either appellant", and there was no evidence that reporting their identities would adversely affect their future rehabilitation.

He added: "The reality is that anonymity lasts only until 18 years of age and both appellants face a very considerable term of detention that will stretch long into their adult life.

"The process of reflecting on their dreadful crimes, addressing their offending behaviour and starting a process of rehabilitation will be a lengthy one."

Markham, who admitted murder, used a kitchen knife to stab both victims in the neck. Edwards had denied murder. She claimed to be suffering an abnormality of mental function which impaired her ability to form rational judgments, but was found guilty after a trial.

Sentencing judge, Mr Justice Haddon-Cave, told them: "The killings were brutal in the form of executions, and both victims, particularly Elizabeth Edwards, must have suffered terribly in the last minutes of their lives.''

Detective Superintendent Martin Holvey, of Lincolnshire Police, said in a statement: "The murders of Elizabeth and Katie Edwards were horrific and brutal and the whole country shared a sense of shock that two juveniles, who were only 14 years old at the time, could have carried out such a horrendous act.

"I'm sure that sense of disbelief and horror will be deepened now it is known that it was Elizabeth's own daughter who was responsible for plotting with her boyfriend to carry out the murders."